This invention relates to a process and device for the disposal of wasted plastics of polyolefins such as polyethylene and polypropylene. More specifically, the invention relates to a process for disposing of plastic waste by combusting a part of the plastic and thereby converting it into an absolutely innoxious gas free from soot and other foreign matter and, at the same time, converting the greater part of the plastic into hydrocarbons useful as fuels and industrial raw materials by utilizing the heat resulting from the aforesaid combustion of a part of the plastic, and to a device used for practicing the process.
The disposal of plastic waste has come to pose a serious problem to the community in recent years in consequence of the incessant increase in the quantities of plastics used. Quantitatively, plastics of polyolefins such as polyethylene and polypropylene account for the majority of the plastics being discarded. Such wasted polyolefinic plastics are generally left to mingle with ordinary trash and then burnt in an ordinary trash incinerator.
When a polyolefinic plastic is burnt in an ordinary incinerator, the plastic is fused and deposited in a form resembling molten gelatin on the grate to obstruct the flow of air. Further, the internsive heat generated from the burning plastic tends to fuse the grate or damage the incinerator proper.
It is technically difficult to have such plastic burnt completely in the ordinary incinerator. The incineration of waste plastic, therefore, entails occurrence of incompletely burnt gas and soot and eventually pollutes the atmosphere.
Various incinerators designed exclusively for the combustion of waste plastics have been suggested with a view to solving the difficulties mentioned above. They invariably have both merits and demerits and none of them have yet been put to effective use.
Attempts have also been made to obtain useful petrochemical raw materials from wasted polyolefinic plastics as the starting materials. For example, research is under wasy on a process of obtaining heavy oil, light oil, kerosene, ethane and so on by thermally decomposing such plastic waste. This process has not yet been materialized because residue from thermal decomposition accumulates within a thermal decomposition unit and changes the operating conditions of said unit from time to time, because products of thermal decomposition are difficult of separation, because continuous operation of the unit for a prolonged period is difficult to achieve, and so on.
A primary object of this invention is to provide a process for completely combusting a part of polyolefinic plastics, particularly wastes thereof, and thereby converting them into an innoxious gas perfectly free from suspended matter and obtaining useful hydrocarbons from the remaining greater part of said polyolefinic plastics by utilizing the heat generated by said combustion.
Another object of the present invention is to provide a highly effective device for practicing the process described above.